Terpolymers with an ethylene weight per cent of over 65 have larger crystalline areas and therefore behave like thermoplastic elastomers. These have a strong resistance to tearing, even in their un-cross-linked state.
The diene content of commercial products is between 2 and 12 weight per cent, corresponding to a proportion of 3 and 16 double bonds per 1,000 C atoms. A higher diene content causes faster cross-linking, greater solidity and less residual deformation. The resistance to ageing, weathering and ozone, on the other hand, dwindles as the diene content rises.
Therefore, depending on the requirements in hand, the right mixture needs to be produced in order to deliver the properties needed, such as higher rigidity or resistance.
Maag Pump Systems has been familiar with the use of EPDM for many years. Maag’s largest gear pumps in the Polymer-polyrex series are used in the manufacturing of these rubber-like applications. In order to develop EPDM films further, solutions for batch operation, small plants and laboratory solutions are available as innovation drivers in order to facilitate the testing of new methods and procedures on a small scale. This experience can later be transferred in a targeted manner to mass production. Industrial pumps made from stainless steel with a special, wide inlet geometry are particularly ideal for these types of laboratory solution.
For removal from the reactor, we use the heated version of the therminox-V pump size 28/28 (TX-V 28/28) which has recently been developed by Maag. This gear pump features a special inlet geometry. The design facilitates the removal of highly viscous fluids, such as pre-polymers (up to 4 million mPa/s) under vacuum.
The pump is directly flange-mounted on the suction side flange on the reactor in order to keep the NPSH as small as possible. The pump housing is the only thing that reveals that the pump is suitable for the toughest, corrosive applications. When developing this test system for EPDM manufacturing, not only did process temperatures of 150°C need to be taken into account for this special design, but so too did a viscosity of up to 1.7 million mPa/s at an NPSH of 5.5 mbar, an inlet pressure of 5.2 bar and an outlet pressure of 10.2 bar. For this reason, Maag used shafts made from 1.4112 stainless steel and bronze-aluminium bearings for this customer-specific application. The shafts and bearings can withstand the process parameters of pressure and temperature.
Excellent emergency running properties were also needed. The design and components ensure an exceptionally durable gear pump. A gland packing is used as the seal, which offers first-class characteristics in terms of simple maintenance. In order for the process to be run with the exclusion of an atmosphere, and in order to prevent reaction of the EPDM medium with air, the seal was made up of a locking, spring-loaded and adjustable packing.
Another advantage of the use of an adjustable seal is the prevention of "bearing pick-up" at high pressure, caused by inadequate lubrication. This pump series has been developed especially for highly viscous media and prepolymers with a low inlet pressure for use in laboratories and small plants. The example of EPDM is just one of many and shows the varied practical applications of the V series from Maag.
